Damage from reactive free species (ROS), including free radicals, occurs in brains of patients with Alzheimer's Disease (AD) studied at autopsy. Whether abnormal oxidative processes are inherent properties of AD cells that promote the pathology or are secondary to neurodegeneration is unknown. The answer will have important therapeutic implications. For several reasons, the best system in which to test whether AD cells have an inherent altered ability to handle oxidative stress is cultured fibroblasts from AD patients and appropriate controls. The use of these cells enables testing for the effects of AD-related genetic mutations on dynamic processes in cells that have the same genetic background in which the disease is expressed. AD/control differences in cultured cells reflect inherent properties of these cells (i.e., the observed differences are not secondary to neurodegeneration, diet or drugs). Our studies with fibroblast cell lines from multiple individuals bearing a particular presenilin-1 AD mutation reveal abnormal ROS metabolism in AD cells supporting the possibility that abnormal ROS are part of the cellular response in AD, rather than a non- specific consequence of neurodegeneration. Fibroblasts from transgenic mice bearing AD-causing mutations will be used to test whether AD-causing mutations affect human and mouse fibroblasts similarly, and if changes in fibroblasts are predictive of changes in brain. The proposed experiments will test the following three component hypothesis: (1) Cells from AD patients handle oxidative stress differently than control cells. (2) the nature of the abnormality in ROS metabolism varies between groups bearing different AD- causing gene mutations in presenilin. (3) Abnormalities in ROS metabolism underlie previously reported AD related changes in calcium homeostasis, mitochondrial function and amyloid-beta- peptide production in fibroblasts. Evidence in favor of this hypothesis would imply that different AD gene-defect groups will best respond to specific types of antioxidants, and that the appropriate antioxidant therapy for a particular patient could be determined in studies of cultured cells from that patient.